Nowadays the use of renewable energies is common for electricity generation, being wind power one of the most efficient among them. The use of wind power makes it possible to obtain electricity from the wind using wind turbines, which basically comprise a tower, a nacelle which houses a rotary electric generator and a rotor formed in turn by at least two blades.
In wind turbines of those known as multi-Megawatt, there is a market trend towards power conversion systems without the use of multiplier, which means that the rotation speed is low and, therefore, the torque developed is, on the other hand, very high.
The dimensions of a wind turbine—diameter and height of the tower—depend on the torque developed, being interesting in general to increase the diameter in relation to the height to optimize the weight and the cost of the active parts, i.e. the copper, the magnetic material and, where applicable, the permanent magnets. Another factor that affects the dimensioning of the wind turbine is heating. The temperature affects the degradation of the wind turbine insulation and, in the case of wind turbines with permanent magnets; it may cause the loss of magnetization.
There are various alternatives for the cooling of the rotary electric generators used in the wind turbines.                Heat dissipating fins. The electrical machine casings often have fins which favour the dissipation of the heat generated therein. Said fins favour the cooling of the generator exterior by convection.        Air forced cooling. It uses fans to force air circulation through the air gap, favouring cooling by convection. Cooling levels achieved are greater than with the simple use of fins.        Liquid cooling. It is common that a fluid cooling circuit is installed, inside the stator crown. These solutions also incorporate external radiators for the dissipation of heat evacuated by the circuit, wherein the radiators may also be cooled by ventilation.        
United States application US2012/0091837 shows an illustrative example of a large number of solutions that propose a liquid cooling system applied to an electric generator of a wind turbine, where the generator comprises a stator equipped with a liquid cooling system, by a plurality of tubes (or holes) in longitudinal direction disposed in the periphery of the stator, wherethrough a coolant fluid can flow, forming a meandering closed circuit.
Furthermore, the United States application US2007/0024132 has the object of a wind turbine generator, comprising a stator equipped with a magnetic core which crown is disposed circumferentially around a longitudinal axis and the teeth of which extend radially from the crown. A plurality of coils is disposed on the teeth. Said generator, has a cooling circuit in connection with a plurality of ducts configured to transport a coolant fluid which, in an embodiment, traverse the magnetic crown of the stator. In an alternative embodiment, a space is disposed between adjacent coils wherein a cooling duct is located.
This cooling system has a series of disadvantages. The first one is that it does not provide enough cooling to the ends of the coils, which on occasions may be of large dimensions and which considerably increase the generator dimensions, as they require a free space between the coils designed to house the cooling ducts that reduce the free space for the copper in the conductors.
Additionally, European application EP2124322 relates to a system for generating power comprising a superconducting generator which in turn includes an armature assembly equipped with a body portion, a tooth portion (having a front surface and a rear surface), a slot partially defined by the body portion and the tooth portion, an armature bar engaging the slot, and a cooling cavity partially defined by the tooth portion, communicative with the front surface and the rear surface, traversing the tooth portion and configured to carry cooled air or house coolant fluid ducts.
Said invention provides a better use of the space than the previous one but without providing a suitable solution to the problem of cooling the coil ends. The need has been detected for describing a cooled rotary electric generator so that it resolves said problems of the state of the art.